Yong Ho Chin

Development of 10 MW L-Band Multi-Beam Klystron (MBK) for european X-FEL project

A 10 MW L-band multi-beam klystron (MBK) has been developed and tested by Toshiba, Japan for the European XFEL and a future linear collider projects. The Toshiba MBK has six low-perveance beams operated at low voltage of 115 kV (for 10 MW) and six ring-shaped cavities to enable a higher efficiency than a single-beam klystron for a similar power. After the successful acceptance testing at the Toshiba Nasu factory in March 2006, attended by DESY staff, the final acceptance test was done at DESY laboratory in June 2006. In these tests, the output power of 10.2 MW, more than the design goal (10 MW), has been demonstrated at the standard beam voltage of 115 kV at the RF pulse length of 1.5 ms and the beam pulse of 1.7 ms at 10 Hz. The efficiency was 66%. The robustness of the tube was also demonstrated by being operated continuously more than 24 hours above 10 MW. Total time of operation on the test stand at DESY already exceeds 750 hours (up to date February 4, 2007). A horizontal version of the Toshiba MBK is now under construction.

Development of Toshiba L-Band Multi-Beam Klystron for European XFEL Project

A 10MW L-band Multi-Beam Klystron (MBK) is under development at Toshiba, Japan for the European XFEL and a future linear collider projects. The design goals are to have 10MW peak power with 65% efficiency at 1.5 ms pulse length at 10Hz repetition rates. The Toshiba MBK has six low-perveance beams operated at low voltage of 115kV (for 10MW) to enable a higher efficiency than a single-beam klystron for a similar power. The prototype-0 has been built and is now under testing. At the first step, it was tested without RF and operates stably at the cathode voltage of 115KV at 1.7ms pulse length at 10Hz repetition rate with beam transmission of better than 99%. No spurious oscillation was observed. The testing is now progressed with RF on. Up to date, the output power of 10.3MW has been demonstrated at the beam voltage of 115kV with efficiency of 68.4% at the RF pulse length of 1ms at 10Hz. The testing is under way to increase the RF pulse length to the goal value of 1.5ms. This paper summarizes the design and the testing results.

Rigorous formulation of space-charge wake function and impedance by solving the three-dimensional Poisson equation

In typical numerical simulations, the space-charge force is calculated by slicing a beam into many longitudinal segments and by solving the two-dimensional Poisson equation in each segment. This method neglects longitudinal leakage of the space-charge force to nearby segments owing to its longitudinal spread over 1/γ. By contrast, the space-charge impedance, which is the Fourier transform of the wake function, is typically calculated directly in the frequency-domain. So long as we follow these approaches, the longitudinal leakage effect of the wake function will remain to be unclear. In the present report, the space-charge wake function is calculated directly in the time domain by solving the three-dimensional Poisson equation for a longitudinally Gaussian beam. We find that the leakage effect is insignificant for a bunch that is considerably longer than the chamber radius so long as the segment length satisfies a certain condition. We present a criterion for how finely a bunch should be sliced so that the two-dimensional slicing approach can provide a good approximation of the three-dimensional exact solution.

Extension of napoly integral for transverse wake potentials to general axisymmetric structure

The Napoly integral for the wake potential calculations in the axisymmetric structure is a very useful method because the integration of Ez field can be confined in a finite length instead of the infinite length by deforming the integration path, which reduces CPU time for the accurate calculations. However, his original method could not be applied to the transverse wake potentials in a structure where the two beam tubes on both sides have unequal radii. In this case, the integration path needs to be a straight line and the integration stretches out to an infinite in principle. We generalize the Napoly integrals so that integrals are always confined in a finite length even when the two beam tubes have unequal radii, for both longitudinal and transverse wake potential calculations. The extended method has been successfully implemented to ABCI code.

ABCI progresses and plans: Parallel computing and transverse Shobuda-Napoly integral

In this paper, we report the recent progresses of ABCI. First, ABCI now supports parallel processing in OpenMP for a shared memory system, such as a PC with multiple CPUs or a CPU with multiple cores. Tests with a Core2Duo (two cores) show that the new ABCI is about 1.7 times faster than the non-parallelized ABCI. The new ABCI also supports the dynamic memory allocation for nearly all arrays for field calculations so that the amount of memory needed for a run is determined dynamically during runtime. A user can use any number of mesh points as far as the total allocated memory is within a physical memory of his PC. As a new and important progress of the features, the transverse extension of Napoly integral (derived by Shobuda) has been implemented: it permits calculations of wake potentials in structures extending to the inside of the beam tube radius or having unequal tube radii at the two sides not only for longitudinal but also for transverse cases, while the integration path can be confined to a finite length by having the integration contour beginning and ending on the beam tubes. The future upgrade plans will be also discussed. The new ABCI is available as a Windows stand-alone executable module so that no installation of the program is necessary.